Schwarzenegger, a Republican, also endorsed a separate ballot proposal Monday to dump political party primaries, a change he said would send more moderates to Sacramento, the state capital.

The endorsement of the stem cell research measure comes at some political risk for the governor, who campaigned against California going deeper into debt when he unseated Gray Davis as governor in last year’s recall election.

“California has always been a pioneer. We daringly led the way for the high-tech industry and now voters can help ensure we lead the way for the bio-tech industry,” Schwarzenegger said Monday.

The endorsement will also put Schwarzenegger at odds with the state Republican Party, which officially opposes Proposition 71, and perhaps the Bush administration, which has limited funding of the research.

“It’s a surprise given the economic challenges facing the state,” said Jack Pitney, a political scientist at Claremont McKenna College who is voting against the measure. “Social conservatives might be unhappy, too, but he was never their favorite anyway.”

Schwarzenegger has said he supports the technology. His father-in-law, Sargent Shriver, is in the early grips of Alzheimer’s disease, which supporters of the measure say could someday be treated with stem cells.

Stem cells are created in the first days after conception and are the building blocks of life. Some researchers hope to turn stem cells into replacement tissue to treat a variety of injuries and disease. But many social conservatives oppose the research because it involves destroying microscopic embryos.

If Proposition 71 passes, it will provide California researchers with nearly $300 million annually for 10 years but cost a total of $6 billion to pay back.

A Field Poll released last week found that 46 percent of likely voters support the measure with 39 percent opposed and 15 percent undecided. The margin of error was 4.3 percentage points.

Schwarzenegger’s endorsement of a separate ballot proposal to dump political party primaries also marks a break with California’s GOP.

“I didn’t come to Sacramento to make the political parties happy,” Schwarzenegger said. “An open primary is an important reform that will lead to more mainstream legislators from each party coming to the Capitol.”

Under the proposal, the two top primary finishers would advance to a general-election runoff, regardless of party affiliation. It would not alter presidential elections.

Critics say the plan would steamroll minor parties off the November ballot while denying party members the right to select their nominees.

“We have more areas of agreement than disagreement (with Schwarzenegger), but in this instance we strongly believe Proposition 62 takes us down the wrong path — a path of less choice for voters,” said Karen Hanretty, a spokeswoman for the state Republicans.

Also Monday, Schwarzenegger announced a plan to protect Pacific waters off the California coast, outlining a series of studies, state programs and legislative actions — some already taken. The plan offers $12.5 million in new funding while calling on state agencies to devise ways to finance new projects.